It's in the Genes!
by GoldenVine
Summary: Little Oliver Holmes was told to expect a sibling some time soon but he only has one question. Unfortunately, no-one seems to wants to answer him.
1. Chapter 1

**A/N - *runs around throwing fluff confetti over everyone* I had an idea! Chapters will be short and sweet and funny. Enjoy!**

**Disclaimer - I don't own Sherlock. I wish.**

Oliver has always been a curious child, _it's in the genes _they said, whatever that meant. He was advanced for a four year old, that was true, but even he couldn't fathom why what he was wearing would influence his curiosity. Yes, Oliver Holmes curiosity knows no bounds and is only really silenced when he has found the answer to his question. That is why the young child was unbelievably agitated when he could not find the answer his question.

_How did the baby get in mummy's tummy?_

It was a logical question. Ever since he was told by his parents to expect a little brother or sister within the next few months he was alight with curiosity. Quite obviously he knew that mummy did not eat the baby because that was gross and Mummy was not a cannon-ball as she had told him. Mummy and daddy were avoiding the question which didn't help the toddler's inquisitive streak. If it was such a big secret he would have to find out.

Oliver Holmes stood in front of the large mirror in his bedroom and clutched his toy tiger (Stripes) to his chest. He puffed himself up to full height and glared at his reflection, he would find out how the baby got inside Mummy if it was the last thing he ever did.

"Oliver, pancakes are ready!" Molly shouted up the stairs to her young son.

He would find out how the baby got inside mummy...but first he would eat his pancakes.

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	2. Chapter 2

**A/N - Here's another one. A big thank you to Rocking the Redhead, MorbidbyDefault and AvoidedIsland for their reviews. Also, to anyone who followed/favourite! These are really fun to write so there will be a few! Enjoy!**

**Disclaimer - I own Oliver but no-one else.**

Sherlock Holmes sat in his study/make-shift lab conducting an experiment on the lungs he had managed to smuggle out of the morgue. Oliver tip-toed up to the door and signalled for Stripes to be quiet. He peeked around the corner of the slightly open door and saw his dad sitting at a workbench.

_Doesn't look too busy, _he decided as he flung open the door and made quite a big entrance for a four year old.

Sherlock looked up from his microscope and greeted his son, "Ah Oliver, did you want something?"

"I want to ask you something" Oliver stated as he shuffled onto a stool opposite his father.

"Ask me what exactly?"

"How did the baby get into mummy's tummy?" Oliver asked staring up at his father with big doe eyes that reminded Sherlock so much of Molly.

"Why would you like to know?" Sherlock queried.

"Because Mummy said the baby was inside her, right, but it must have gotten in there somehow and I want to know how."

"That is a valid point with sound reasoning."

"So, how did the baby get inside?" Oliver asked growing impatient.

"I will not just answer the question Oliver. You are a Holmes, you will need to do research of your own. Think of it as a case, like what I do for my job, do you remember?"

Oliver nodded his head and hugged Stripes tight to him.

"You must gather evidence and then find out the answer for yourself."

"But dad, I'm four" Oliver huffed.

"Well, you have to start somewhere. Now, run along I have an experiment to conduct." Sherlock turned back to his microscope and smirked at his sons determined expression.

Oliver Holmes walked out of the door about to embark on the biggest case of his life.

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	3. Chapter 3

**A/N - Here you go! Thank you to Rocking the Redhead, MorbidbyDefault, rilakjenya, EbonyFox and all who have followed/favourite! It means a lot that people are enjoying reading this story as much as I'm enjoying writing it. Enjoy!**

**Disclaimer - I do not own Sherlock. *sigh* **

Oliver and his assistant Stripes, were pacing the short stretch of the hallway thinking of a place to start their investigation. Oliver came to a sudden halt and smiled, he knew exactly where to start.

First on his hit list was mummy. She was an easy target because she always gave into him, well almost always. His request for a tarantula was a bit out there even if his dad fully endorsed it. She would surely clear up his query as to how the baby got inside her. It was her tummy so she must know how it got there.

"Mummy?" Oliver enquired from his position at the kitchen table.

"Yeah baby?" Molly answered as she finished putting away the dishes.

"How did the baby get inside your tummy?" Oliver asked, swinging his legs gaily.

A loud crash rang out as the plate Molly had been drying slipped from her fingers and dropped to the floor.

Oliver regarded his mother with a strange look, "Why would you ask, Oli?" answered a flustered Molly.

"Well, it is inside you and I just wondered how it got there, since you're not a cannon-ball."

Molly laughed softly, "Cannibal dear. And no I'm not. The baby is growing inside me."

"Yes, but how did it get there?" Oliver pushed.

Molly went red in the face. She was not about to explain the ins-and-outs of sex to her four year old. God knows the kid was already scarred from having Sherlock Holmes as a father, "Well when a mummy and daddy love each other and decide they want to have a family they get together and um, _make_ a baby."

Oliver hummed as he thought about mum's suggestion. _Make _a baby?He'd never thought of that. Do you just make babies out of arts and crafts stuff like he made paintings at nursery? Oliver suspected that mummy had raised more questions than she had answered. He needed some time to think on this new development – he would need to talk to Stripes.

"Thanks mummy!" Oliver shouted as he launched himself off of the chair and hurtled through to his bedroom.

Molly chuckled and bent down to pick up the shards of the broken plate, _let's hope that satisfies him although knowing his father there are many more questions to come._

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	4. Chapter 4

**A/N - Here's a longer chapter because I just love Mycroft, ok? Thanks to Potix, Guest, Kathmak, SpencerReidFan89, daisherz365, Adi Who is Also Mou, MorbidByDefault, ThefadingdaysofMay, Renaissancebooklover108, Rocking the Redhead, CompanionToMisterHolmes, Calicar and patemalah21 for their wonderful review! And a big thank-you to all that have favourite/followed! You guys are all awesome. Anyway, enjoy!**

**Disclaimer - I just checked and unfortunately I don't own Sherlock.**

It was three weeks later and Oliver hadn't gotten any further in his case. He hadn't been able to find any baby making art supplies in the local toy shop and his attempt to bring a baby doll to life was not successful. It was clear that he just didn't have the scientific knowledge to be successful at creating a human being unlike Dr Frankenstein from his favourite book.

Oliver sighed as he was lead to his uncle Mycroft's study. It was time for the fortnightly family visit that had been established when his father had come back to life after his fall, which Oliver would be told about "when he was old enough and not any sooner" according to his mother.

Oliver walked over to his uncle and hugged him tightly. Uncle Mycroft was the best at hugs but rarely ever gave them to other people, only ever to his nephew. The only other person ever to get a hug from Mycroft was Grandma Holmes but that didn't count because she was old and needed the hugs.

"Hello Oliver! Oh, I have something in the garden I want to show you!" announced Mycroft as he scooped up the small boy and carried him out to the flower bed completely ignoring his brother and sister-in-law in favour of the little boy.

"Do you remember the tulips we planted a little while ago?" Mycroft asked setting the boy down beside the flowerbed.

"The yellow ones?"

"Yes, that's right. Do you remember what we put in the soil?"

"Umm, oh yes! Seeds! You said they would grow into flowers" answered Oliver brightly.

"I did indeed! Well look at them now." Mycroft gestured to the row of yellow tulips standing to attention in front of them.

"Wow!" Oliver said as he looked at the flowers. They were still small but they were starting to shoot up towards the sky. They were a brilliant yellow colour and had flecks of orange near the stem. They had grown so much since Oliver had last seen them. Wait a minute! That gave him an idea about his case, "Uncle Mycroft?"

"Yes."

"Do babies come from seeds?"

Mycroft chuckled and ruffled the boy's ebony curls, "No, they don't come from seeds. Whatever gave you that idea?"

"Well, mummy said the baby was growing inside her and the flowers are growing too. They grew from the little seeds we put in the soil so I thought that maybe mummy had eaten a seed and that's how the baby was growing inside her tummy" explained Oliver quite proudly.

"Well, that is certainly a very logical theory however plants are very different to humans. Babies are indeed a miracle of nature much like our golden tulips. They grow from something tiny into a very complex being" Mycroft reasoned as he picked up the small boy again, "Now, I believe that was the bell for lunch."

Oliver thought on what uncle Mycroft had said whilst he was being carried into the house. _So, babies didn't come from seeds but they came from something tiny and then grew bigger. Well, that made sense but it still didn't explain how the baby got in there in the first place. I'll need to tell Stripes about this later._

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	5. Chapter 5

**A/N - It's uncle Greg's turn! Thank you to Rocking the Redhead, Kathmak, Nicolive, Ariena-Rose Eveilebe, Brichisa, MorbidbyDefault, Pinstripes and Buttons, Prisia Lex and patemalah21 for their lovely reviews! Thanks to all follows and favourites! Enjoy!**

**Disclaimer - Nope, still don't own Sherlock.**

"Uncle Greggy!" Oliver shouted as he whizzed past the tired detective dozing on the couch. Sherlock and Molly were away out on a date (Sherlock reluctantly, Molly excitedly) and Greg Lestrade had been left in charge of the energetic four year old.

"Uncle Gregggy get up we are playing aeroplanes!"

"No, no we're not. I told you its bed time" argued the DI resting his head on his hands.

"But mum and dad are out so that means I don't have to go to bed on time!" whined Oliver slowing down his imaginary aircraft and landing it on his makeshift cushion runway.

"Uh uh! You are not pulling that one. Do you remember what happened last time?"

"Mummy told you off" said Oliver glumly.

"Yes and I am not facing your mothers wrath again so upstairs to bed, now!"

After some initial reluctance Oliver sulked his way up the stairs muttering under his breath in a fashion so much like his father.

Once tucked into bed with Stripes firmly under his arm, Oliver was ready for his bed time story.

"Right which one is it this time?" Greg said standing beside a small bookshelf that was crammed with Oliver's favourite tales of dragons, pirates and talking animals.

"The one about the chicken please?"

Greg pulled out a thin red book with a chicken on the front, "This one?"

"Yep" giggled Oliver as he snuggled deeper into Stripes.

"'My eggs were nice, but my chicks are much, much nicer!' The end. Did you enjoy it then?" asked Greg.

Oliver's eyebrows were pulled tight together and he was sucking his thumb thoughtfully. Lestrade had never seen a look of such intense concentration on someone so young.

"Right, well lights out time," Greg placed a soft kiss to Oliver's forehead, "Night night."

"Wait uncle Greggy!"

"Yes?"

"Is mummy going to lay an egg?"

Greg chuckled, "No, she isn't going to lay an egg. She's not a chicken."

"I know that," Oliver pouted, "I'm on a case."

"A case?"

"Yes. Dad says I have to figure out for myself how the baby got inside mummy's tummy and it's like a case. I've been doing research." Oliver said proudly.

"Oh right, I see, "Greg hummed, "What have you found out so far?"

"Mummy isn't a cannibal. The baby is growing inside her and uncle Mycroft said the baby grows from something tiny into something big like flowers but I still don't know how it got there in the first place!" complained Oliver finishing off his spiel with an almighty yawn.

"Well mummy isn't a cannibal and uncle Mycroft is right," Greg knew how to handle this, he had two children of his own and you didn't raise kids without picking up a thing or two, "You see, little one, mummy has an egg inside her and daddy added a special part to it which makes the baby start to grow and that's how it's inside mummy's tummy."

Oliver thought for a moment, "So the egg was already inside mummy?"

"Yes."

"That makes sense."

"Yes, it does. Case closed I would say. Goodnight junior detective!" Greg winked.

Just as Greg got to the door he was stopped by a small, tired voice, "But how did daddy add the special part?"

"That's another question for another day" Greg answered then quickly plugged in Oliver's night light and switched the main light off leaving the door slightly ajar.

Yes he knew how to handle questions but he was not handling _that _question.

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	6. Chapter 6

**A/N - Penultimate chapter! Rocking the Redhead, Zora Arian, MorbidbyDefault, crooney83, Nicolive, Renaissancebooklover108 and Pinstripes and Button for their gracious reviews! And a big thank you to all who followed/favourite. Enjoy!**

**Disclaimer - I don't own Sherlock.**

"Oli, Uncle John is here!" Molly shouted up the stairs.

Oliver bounded down the stairs and flew right into a startled John Watson.

"Oh hello there!" John greeted hauling Oliver up to sit on his hip, "how are you?"

"I'm hungry" stated Oliver frankly.

"Oh well, honest as always," John laughed.

"I'm making lunch," Molly shouted through from the kitchen, "Sherlock's out at the moment John but he should be back in about an hour. Something about his brother and world war three. I didn't ask."

"Ah, probably best not too. Where are you pulling me Oli?" John asked as he was dragged rather forcefully up the stairs by a determined four year old.

Oliver pushed him into his bedroom and sat him down at the plastic table and chairs before shutting the door and settling opposite him. John was bewildered as to what the small boy wanted but he had told Molly not to ask when it came to a Holmes so he had better take his own advice.

"So where is Stripes today?" John asked looking around for the boy's ever-present sidekick.

Oliver looked pointedly at the bed, "He's asleep. We were up late last night."

"Oh, why were you up late?"

"Thinking."

"Mmm I see, what about?"

"My case" shrugged Oliver.

"Your…case?"

"Yes."

"What case would that be?" enquired John.

"I wanted to know how the baby got inside mummy's tummy but I know that know. She has an egg inside her, uncle Greggy told me. Now though I have another question" explained Oliver.

"Oh, ok. You know I sometimes help your dad on his cases so maybe I can help you?" suggested John.

Oliver thought for a moment. John is older and he has experience being on cases. Yes, he might be able to help. Oliver nodded, "Ok, how did daddy add the special part to mummy's egg so that the baby would grow in her tummy?"

John was silent. He had expected a question like this at some point however, he did not expect to be the one faced with it.

"Well, when a daddy and mummy love each other," John started, "they get together and make a baby."

"Yes I know that bit. Mummy told me but I don't understand" Oliver stated looking up at John earnestly.

"Well mummy's egg and daddy's special part come together and make a baby."

"Alright, but how did daddy get the special part to mummy because the egg is already inside her?"

"Well, ehm, shouldn't you ask your dad?" John wriggled uncomfortably in his plastic chair. He didn't have any experience with little kids, how much should they know at this stage?

"No. He said I had to find out myself. I'm a Holmes." Oliver stood up and collected Stripes from the bed.

"You certainly are but you found out the answer to the first question, is that not enough?" John reasoned.

"I suppose so" shrugged Oliver however he was not entirely satisfied. He would need to find out how the special part got inside before he could announce case closed. Maybe his dad performed an operation on mummy? That seemed a lot of hassle though just to get another baby. They already had Oliver. Wasn't one enough?

Oliver sighed and led Stripes down the stairs to lunch. His rumbling tummy needed attention and then he would finish the case and he needed to finish it soon before mummy's tummy exploded.

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	7. Chapter 7

**A/N - I do apologise for the delay, this should have been posted ages ago! Thank you to SpencerReidFan89, Potix, Rocking the Redhead, MorbidbyDefault, Thestarlitrose, Dust And Bones, Renaissancebooklover108, Nicolive, Snarkland78, Pinstripes and Buttons, GreenEyedLiz, Guest x 2, Kathmak and Owl Lady for their wonderful reviews! And of course thank you to all that followed/favourite! Here's the last one! It doesn't pan out how you would expect but don't hate me! Enjoy!**

**Disclaimer - I checked again but I still do not own Sherlock - I only own Oliver (and Stripes!)**

Oliver delved deeper into Mrs Hudson's couch and wriggled around under the patchwork quily the elderly lady had draped over him.

"Now, I'm sorry I didn't have time to make up the camp bed but labour does tend to be surprising!" Mrs Hudson giggled as she sat carefully on the end of the couch.

"Mummy's having the baby just now?" Oliver asked.

"Yes dear and I'm looking after you until we can go and see the new baby." She bent over and tickled Oliver's stomach making him squeal in surprise.

"Mrs Hudson stop being silly!" chided Oliver.

"Oh, you're just like your father."

Oliver looked away and sighed audibly. The mention of his father had reminded him of his problem, "Is something the matter dear?"

"Yes."

"Do you want to tell me about it?" suggested the elderly woman clearing a stray curl from his forehead.

"It's just that mummy is having the baby and I haven't solved my case yet!"

"Ah, yes the case I've heard so much about. Your mummy told me you were trying to find out how the baby got inside her, hmm?"

"No I found that out" stated Oliver.

"And?" prompted Mrs Hudson.

"She has an egg inside her" said Oliver proudly.

"Yes, that's right and mummy's egg grew into the baby," Oliver nodded his agreement, "so what's the matter?"

"Uncle Greggy said daddy added a special part to help the baby start growing and I want to know how he got it into mummy since the egg was already inside her."

"Well that is a conundrum" sighed Mrs Hudson shaking her head at the befuddled little boy.

Oliver huffed at the older woman. He was getting frustrated with this case. Why wouldn't anyone just tell him?

"I think the key to the answer is your age" stated Mrs Hudson.

"What?" Oliver asked. What did his age have to do with anything?

"Well, as you get older you learn things about life. Life teaches you things and you have to accept its lessons. Do you trust me Oliver Holmes?"

"Yes, you give me lots of cake."

Mrs Hudson chuckled at the boys reason for trust, "Well, trust me when I say this, you will find out how daddy added the special part when you are older, ok?"

Oliver huffed and wriggled and sighed. He found out the answer to his original question which meant that technically he did solve the case and that meant that daddy would be proud of him. If Mrs Hudson was right and calculating that he was advanced for his age he would only need to wait another 2 years to find out the answer and luckily, he had inherited his mother's patience so it really wasn't that long.

After 5 minutes of thinking he muttered a quiet ok and said goodnight to Mrs Hudson who patted his head affectionately and turned out the light.

"Someday that boy's curiosity will get him into trouble" she tutted as she made her way into her own bedroom intent on a good nights rest.

The next morning Oliver Holmes was dragged along a sterile hospital corridor by Mrs Hudson and into a small room where his three uncles and his dad were crowded around a hospital bed. When he got closer he could see his mother sitting up on the bed with a small blue bundle in her arms.

"Hello, Oli!," smiled his mum brightly, "come and meet your new baby brother!"

Oliver approached the bundle with caution. He was glad he had left Stripes at home as he didn't do well with strangers. He peered over his mum's arms at the sleeping baby. He was tiny, Oliver noted, and very pink. The baby had a few patches of brown hair and his fingers were really tiny and curled into fists around the blue blanket he was wrapped in.

He looked around at the adults in the room who were cooing and smiling at him and his new sibling. The baby was quite cute he supposed but not quite as lively as he had hoped. Suddenly a spark of curiosity flared in the small boys head.

"I have a question!" Oliver said as he looked at his baby brother and then to the adults.

Each adult looked at Oliver's shining bright blue eyes dreading the question that was to come. The room was silent and the air tense as Oliver formed the question in his head.

"How did the baby get out of mummy's tummy?"

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